Apparently I need a new PCM

[tRidiot]

So my '04 Tahoe I am told has a bad PCM. Back in April I had problems with my truck dropping into 'limp mode' after just a couple of minutes of driving. Took it to a local shop, very reliable, reputable, honest guys, in my opinion. Also very busy (not a coincidence). They had it a few weeks, told me initially they thought it was something with the fuel system, and I had some kind of fuel sensor or thingiemajiggy in the fuel line that wasn't responding, about $750, they thought this could be it. We replaced it - didn't fix things. So they took it back out, put the old one back in, didn't charge me. Yay. Then they finally were able to duplicate the problem when driving with the computer hooked up and told me it was something with the fuel system, they thought the throttle body. Later the throttle body control module. All in all, $900 later, my truck was running and everything worked.

For 5 months.

So now, here I am, same problem again - sheisse. I know that 'limp mode' can be triggered by all manner of things. This same shop has a 1 month wait now before they can do anything with it, so it took it to another guy I trust fairly well. He has had it a week - took me an hour to limp it over there, kept having to pull off the road, shut it down, let it sit for a couple minutes turned off and it would reset and drive another few minutes before it 'limped' again.

So he's tested the wiring and such, says same thing, something in fuel system/delivery, etc. He initially thought the throttle body might have gone bad again. Now he calls, says he's traced the two wires that control the TB, they seem intact, but when he plugs the PCM back in, it immediately pops his connection, with everything off - so he thinks the PCM has a short or bad spot in the connection for this system (the throttle body).

I have an HP Tuners MPVI2, which I bought some time ago, never hooked up and used - 2 credits with it as well.

I guess my question is, will I be able to pull my old PCM, download the tune from it, since I never did before, and then put it on another PCM I find somewhere? Or is the short in the PCM likely to prevent my from getting my tune off it?

<complication> This is not the original tune. I replaced the motor with a 6.0 and the seller took my PCM (I shipped it to him) and he put what he said was an Esky 6.0 tune on it. This was noted by both shops, that it looked like it had been reprogrammed, which it was. If I can do this myself, it might be a reasonable fix, right? Couple hundred bucks for a PCM somewhere, then use the HP Tuners HPVI2 to program it, and *boom*, I'm off and running again?

This truck is really getting me down. Almost 300k miles and it seems like it's sitting or in the shop more than it's been running the last few years. <sigh> Love to have a new vehicle, but no way these days. Unfortunately, my job doesn't pay like people think it does. <sigh>

 

[Joseph Garcia]

I am not familiar with HP Tuners, but with a Black Bear tune, you can retrieve the tune from the PCM and store it until needed.

With a replacement PCM, I 'think' that you will need to program it to your VIN.

Other members of this Forum much more knowledgeable than me in this area will chime in.

 

[tRidiot]

I see PCMs on Ebay saying programmed to my VIN - but I also assume this will have a stock 5.3 tune, which won't work for me, as I now have a 6.0, AND I will need to be able to activate the electric fans I had installed years ago - though I assume I COULD do this with my HP Tuner system after the fact, right? I had been meaning for 2 years to get into mine to reprogram it to correct for wheel/tire size and see if this fixed my speedo being off, but never got around to it.

I see on HP Tuners repository a 2004 Cadillac Esky 6.0 tune I could download, so I guess that might work. Do I just buy a PCM on Ebay and send them my VIN and then try to put the 6.0 tune on it, install and hope it runs?

 

[mattbta]

I see PCMs on Ebay saying programmed to my VIN - but I also assume this will have a stock 5.3 tune, which won't work for me, as I now have a 6.0, AND I will need to be able to activate the electric fans I had installed years ago - though I assume I COULD do this with my HP Tuner system after the fact, right? I had been meaning for 2 years to get into mine to reprogram it to correct for wheel/tire size and see if this fixed my speedo being off, but never got around to it.

I see on HP Tuners repository a 2004 Cadillac Esky 6.0 tune I could download, so I guess that might work. Do I just buy a PCM on Ebay and send them my VIN and then try to put the 6.0 tune on it, install and hope it runs?

Find the service number for your PCM and buy one on eBay. You can find ones that haven't been programmed for cheaper which you don't need VIN programmed since as you say, you have a 6.0 tune.

I'm not sure how HPTuners works on PCM replacement, you would need to research that. No clue if you have to get more credits. However, I used my VCX Nano and PCM Hammer to "clone" my OEM PCM to an eBay one when I was turning on my e-fans.

Were the connectors or pins on the PCM crusty with green nasties indicating water intrusion? I'm not wholly convinced it is the PCM, but if you don't need more HPT credits, it might be the cheapest option in the parts cannon. Lots of posts about the TAC/TB harness/wiring but sounds like your trusted guy thinks they're ok.

My 2004 Tahoe PCM:

 

[Mudsport96]

The only problem I see is that you drove it there and after he started diagnosis is when popping fuses. Am I getting that right?

If so it seems more likely that it is a harness issue than a ecm issue. Do you have the ability to get your hands on an ecm? If so you could easily swap it in and see if the fuse pops. If not then the ecm could really be the issue.
Also the throttle body has 8 wires not 2. So is he sure he found the right harness?

 

[Jimmyy]

Not saying this is your issue. But in the video it shows how bad wires can cause problems.

 

[strutaeng]

You can save your vehicle's tune to your computer and then re-write to the new PCM.

Watch a YouTube video on how to do it, it's not that difficult. Did your HP Tuners already come with the 2 credits required?

 

[tRidiot]

You can save your vehicle's tune to your computer and then re-write to the new PCM.

Watch a YouTube video on how to do it, it's not that difficult. Did your HP Tuners already come with the 2 credits required?

I do have the 2 credits on my HPTuner.

I'm not too sure abiut the other stuff. He said testing the continuity everything was fine going both directions to/from the throttle body. It was only when he reconnectwd the computer even with power off that it was tripping his circuit test he had set up, or something. I havent gone over it in super detail with him, it was just via a quick phone call. I'm not sure what else to do... other than maybe a Molotov into this danged truck. (sigh)

Working on some business deals, maybe late next year I'll be able to get something new(er).

 

[tRidiot]

The only problem I see is that you drove it there and after he started diagnosis is when popping fuses. Am I getting that right?

If so it seems more likely that it is a harness issue than a ecm issue. Do you have the ability to get your hands on an ecm? If so you could easily swap it in and see if the fuse pops. If not then the ecm could really be the issue.
Also the throttle body has 8 wires not 2. So is he sure he found the right harness?
View attachment 412744

I drove it to the shop - barely. It would run a couple minutes, then go into 'limp mode' then I would have to pull over, turn it off, let it sit a minute and start it back up. A couple of tries on/off, it would run ok, then another mile or so and repeat. Took me about 20-25 minutes to get like... 3-4 miles. I guess. He said they couldn't get it to run to get it into the shop, they had to push it. Not sure how many times they tried starting it/turning it off.

So my question is... if I buy an UNPROGRAMMED PCM off Ebay, can I use my HP Tuner to 'clone' the PCM I have onto it? So I don't need to have anyone program it for my VIN? I mean, I'm not sure what all they're doing for the 'programming' from Ebay. They want your VIN - does this just mean they look up your original equipment and put a generic 5.3 from that model year on it? So if I have changed my motor to a 6.0, that won't work. Obviously would need a 6.0 tune. I can download a generic 6.0 tune for a Suburban from HP Tuners' database. If this is all I need, I don't mind doing that - I can turn on the fans myself when I program it, right? I don't really NEED to clone the tune from my current computer (which was reprogrammed by the guy who sold me the motor).

Like I said, I've had this tuner for a couple years now (well, 18 months anyways) and never did anything with it. But I have a harness adapter to do everything outside the vehicle, as well.

If I'm understanding things correctly - buy a PCM from Egay, then put the HP Tuners basic 6.0 tune on it, swap into my truck and drive away - I hope. If it is INDEED a mechanical computer issue, like an internal contact or diode or something, this should work? I mean, I understand this may not fix the issue - but if this will give me a functioning computer for a couple hundred bucks, this will at least remove that from the list of possible problems, yes? I've just never DONE a computer retune, so I'm asking if anyone can tell me this is how you do it, or maybe point me to where I can look? I need to go check out HP Tuners page, too... I think they have a forum as well. I was just at a conference all weekend so I haven't had a chance to look at anything - that is my next step.

Thanks for any help.

 

[Mudsport96]

Yes a basic 6.0 tune would work. They probably need the Vin to match the anti theft. But you can turn that off with hp I think